An IP multimedia subsystem (IP Multimedia Subsystem, IMS for short) is an IP-based multimedia service communication network. An IMS network uses an IMS core network subsystem (IP Multimedia Core Network Subsystem) to perform service control, and a packet-switched network or a circuit-switched network is used as an access network to provide bearers for signaling and media transmission. Thereby, service control is separated from bearers, and a unified and flexible support platform is provided for IP multimedia applications.
When an IMS user moves between different access networks, in order to ensure a good user experience, it is required that the ongoing IMS session should not be interrupted, that is, the IMS session continuity (Session Continuity, SC for short) should be maintained. Similarly, when the user transfers some or all media streams of the ongoing IMS session from a user equipment (User Equipment, UE for short) to another UE, in order to provide a good user experience, it is also required that the media streams of the session should be continued and not interrupted in the transfer process. Service continuity implemented for some or all media streams of the IMS session in an inter-UE transfer (Inter-UE Transfer, IUT for short) process is a part of the IMS session continuity.
One certain end of a session may include one or multiple UEs. When one end includes multiple UEs and the multiple UEs communicate with a same UE at the remote end, sessions of the multiple UEs form a collaborative session. Among the multiple UEs in the collaborative session, there may be one or multiple controller UEs (controller UE) and one or multiple controllee UEs (controllee UE). The controller UE may control the UEs in the collaborative session and the media streams on those UEs. In the collaborative session, media streams may be transferred from one UE to another UE, or transferred to a UE outside the collaborative session, and the UE joins the collaborative session after completion of transfer.
A service centralization and continuity application server (Service Centralization and Continuity Application Server, SCC AS for short) is a key function entity in the IMS session continuity system, interacts with an IMS user through a serving call session control function entity (Serving Call Session Control Function, S-CSCF) for short), and performs a core SC service logic control For easy description, the service centralization and continuity application server is referred to as continuity application server for short in the present invention. In a process of registering with the IMS domain, the IMS user further performs third-party registration with the SCC AS that the UE belongs to, and IMS users under different subscriptions may belong to different SCC ASs.
In the collaborative session, each UE may have multiple access legs (access leg) presented through the SCC AS that the UE belongs to, and the multiple access legs are anchored to the SCC AS of the controller UE, and a remote leg (remote leg) is presented to the remote end. The SCC AS that the controller UE belongs to is referred to as a controller SCC AS, and the SCC AS that the controllee UE belongs to is referred to as a controllee SCC AS. The controller SCC AS stores information about each UE and media on each UE in the collaborative session. The media transfer mode in which a UE transfers media on other UEs to the UE itself by sending a request is referred to as a “pull mode”, that is, a pull mode. The UE that sends the request may be a controllee UE in the collaborative session, or may be a UE outside the collaborative session.
In a session discovery (session discovery) phase of the UE, if a certain discovered target UE is a controllee UE in the collaborative session, and the controllee UE and the controller UE are UEs under different subscriptions and belong to different SCC ASs, after a pull mode media transfer request is sent to the SCC AS that the target UE belongs to, an media transfer operation cannot be completed because the controllee SCC AS is not authorized to transfer media. Therefore, the prior art is limited as to the media transfer operation between UEs, and cannot ensure the session continuity reliably.